Air-spring flexible members are sealed at their two open ends by means of attachment parts and are attached via these parts to the vehicle. Various types of sealing connections are known in order to obtain a tight seat of the ends of the air-spring flexible member on the attachment parts. The attachment parts can have conical sealing seats on which the air-spring flexible member is seated with corresponding conical sealing beads. Beadless air-spring flexible members are mounted with clamping rings to the attachment parts. Air-spring flexible members having sealing beads which can be clamped are tightly clamped to an attachment part configured as a flange plate by bending over the edge of the plate. Air-spring flexible members having clampable sealing beads and beadless air-spring flexible members are supplied to the vehicle manufacturer with the attachment parts mounted.
The air-spring flexible members complete with the attachment parts are built in between the vehicle frame and the vehicle axles with the upper attachment part being usually configured as an attachment plate having projecting attachment bolts. The upper attachment part is connected to a support member of the vehicle frame. The attachment bolts are welded with their bolt heads to the inner surface of the attachment plate. It is also possible to provide the attachment plate with embedded bushings, for example, welded bushings in which threaded bolts are threadably engaged when the vehicle is assembled.
Air springs having a flexible member made of elastomeric material have proven successful for many decades as a load controllable spring element in the manufacture of vehicles. Notwithstanding this positive performance of the air springs, efforts are undertaken in order to increase the service life and the safety during use of the air springs. For this purpose, attention is mostly directed to the development of special elastomeric materials.
New investigations have shown that a further reason for possible leakage of the air springs in long-service operations can also be the attachment parts. It was determined that the effects on service life were in the area of the attachment of the attachment part to the particular vehicle part. In the area of the bolt head of the attachment bolts, a stress concentration results because of the cross-section interface which, for the dynamic load of the attachment part, greatly reduces the durability of the attachment region because of the spring operation. For this dynamic loading, the arcuate deflections cause movements and slight lift-off actions of the plate-shaped attachment part with respect to the vehicle frame support member to which the air spring is attached. If the stationary bolt head or the embedded bushing are also welded, the disadvantageous consequence of stress concentration is further increased because of the weld influence zone so that a fatigue fissure can develop in this zone. This fatigue fissure runs from the weld seam into the attachment plate causing leakage to occur.